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New dicamba restrictions

November 1, 2018 7:31 AM

Blog Post

Updated on November 2, 2018

I feel obligated to write something about EPA’s dicamba announcement, but will confess at this time I still have several questions that I’m seeking answers for. But here are my initial thoughts regarding the new approach to dicamba management.

1. 45 days after planting. I’m not sure if this restriction replaces the previous restriction that limited applications up to and including the R1 soybean stage. Regardless, I see very little value to this new restriction. According to USDA-NASS Crop Progress reports, the 5-year average for Iowa soybean planting is 51% planted on May 20. Thus, applications would be allowed into July for much of Iowa’s soybean acres. In 2017, 90% of dicamba misuse complaints to IDALS were associated with applications made after June 15. I believe a date restriction would be more appropriate, a date in mid-June would be my preference.

The label includes a growth stage restriction, and has been moved earlier in the season. The initial labels stated that dicamba could be applied up to and including the R1 growth stage, now it states that dicamba must be applied prior to beginning bloom (R1) or no more than 45 days after planting, whichever comes first.

2. Certification status. Persons under the supervision of a certified applicator will no longer be allowed to apply dicamba on Xtend soybean. In 2017, the breakdown of applicators responsible for misuse complaints in Iowa from dicamba on Xtend soybean was 22%, 40%, and 38% for certified commercial, certified private, and uncertified private applicators, respectively. I don’t know what percentage of the Xtend beans were sprayed by the various classes of applicators (i.e. did commercial applicators spray 80% of the dicamba on Xtend crops), but these numbers don’t suggest the classification of applicator has a big influence on the likelihood of off-target movement. The new products were changed to Restricted Use for 2018, so uncertified applicators could not apply dicamba on Xtend soybean in 2018.

3. Endangered species. I assume this restriction will pertain to both plants and animals. Iowa doesn’t have any plants listed as endangered, there are five species classified as threatened. However, there are several animals listed as endangered, and a quick perusal of the list suggests the majority of Iowa counties have at least one endangered species. Thus, if animals are included in this restriction most fields in Iowa would require the 57-foot buffer along field edges (the 110 ft downwind buffer is still in play regardless of endangered species).

The label refers users to an EPA webpage dealing with endangered species. At this time the bulletins associated with dicamba products have not been posted. I am still not aware whether restrictions will deal only with endangered plants or any endangered organism.

4. Application hours. The previous labels restricted applications to between sunrise and sunset, this has been further restricted to 1 hour after sunrise and 2 hours before sunset. This restriction is intended to prevent applications during inversions. In Iowa I know spraying in inversions has been a problem, but I don’t believe it is a leading cause of off-target movement and injury. This further restricts time available to apply dicamba, making it increasingly difficult to apply the product legally.

As I’ve said before, the EPA is in a very difficult position in regulating this technology – whatever they do is going to be criticized by some people. Unfortunately, I don’t think these new restrictions will have a significant impact on the problems we've seen the past two years. I was hoping for something similar to what Minnesota did in 2018, a date and temperature cutoff for dicamba applications on Xtend soybean. The Iowa Department of Agriculture and Land Stewardship can develop more restrictive approaches to managing dicamba, and I hope they will take this approach.

Dr. Bob Hartzler is a professor of agronomy and an extension weed specialist. He conducts research on weed biology and how it impacts the efficacy of weed management programs in corn and soybean. Dr. Hartzler also teaches undergraduate classes in weed science and weed identificatio...

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